The present invention relates to an optical information storage apparatus using an optical fiber and, more particularly, to an optical information storage apparatus using an optical fiber in an optical information processing apparatus for storing and processing information by using light.
Information processing based on light is expected to overcome the limits of speed and capacity of information processing performed by using only conventional electronic circuits. An information processing apparatus for such processing always requires a storage apparatus.
As a scheme for storing optical information, there is proposed a scheme for storing optical information upon converting light into electrical signals. Prototype optical memory apparatuses manufactured by using various optical device techniques basically use such electrical signals. In contrast to this, as an apparatus using a scheme for storing optical information as light, there is provided an optical information storage apparatus utilizing the transmission delay time of an optical fiber.
FIG. 13 shows the basic arrangement of a conventional optical information storage apparatus using an optical fiber.
Referring to FIG. 13, a loop of an optical transmission path is formed by an optical fiber 3. Optical information is stored, as a time series signal, in the loop, as shown in FIG. 14A. In this case, the length of the time series is determined by the time required for transmission through the total length of the looped optical fiber 3. Information is recorded or reproduced by adding new data to the data in the loop or extracting specific data therefrom through a directional coupler type optical switch 14 using a lithium niobate substrate, as shown in FIG. 14B.
Such a conventional optical information storage apparatus using the optical fiber 3 requires an optical amplification function for compensating for a loss due to transmission. Such a function can be realized by inserting an optical amplifier 15 in the loop, as shown in FIG. 13. Such an optical amplifier, however, generates noise to decrease the S/N ratio of stored information with time. In addition, since there are many elements in the loop, the size of the apparatus becomes large.